Silicon carbide is a ceramic material valued mainly for its high resistance to thermal stress and shock and its exceptional corrosion resistance in high-temperature oxidizing environments. It has also found extensive use in the abrasive industry because of its hardness and wear resistance.
A number of methods of manufacturing silicon carbide have been developed. These methods include, for example, the carbothermal reduction of silica in an inert atmosphere in a vertical furnace which is based on a reaction approximating the following stoichiometric equation: EQU SiO.sub.2 +3 C.fwdarw.SiC+2 CO (gas) (1)
However, it is well-known that the actual reaction mechanism proceeds through the synthesis and subsequent reaction of gaseous silicon monoxide according to the following sequence: EQU SiO.sub.2 +C.fwdarw.SiO (gas)+CO (gas) (2) EQU SiO (gas)+2 C.fwdarw.SiC+Co (gas (3)
A part of the silicon carbide may be formed through a side reaction represented by EQU 2 SiO (gas).fwdarw.SiO.sub.2 +Si (4) EQU Si+C.fwdarw.SiC (5)
Many of the problems previously encountered with the carbothermal reduction process have been addressed and solved by the process disclosed in commonly-owned PCT Patent Application No. PCT/US90/00276 filed on Jan. 11, 1990, to Weimer, et al. The patent application, which is hereby incorporated by reference was published on Jul. 26, 1990, as a PCT application having International Publication No. WO90/08105. Although the invention disclosed in PCT Patent Application No. PCT/US90/00276 is considered to be an exceptional advance in the field of producing silicon carbide, there remained opportunities to improve the process by improving the conversion rates and by making the process more economical.
It is, therefore, a primary object of the present invention to provide a process for making silicon carbide by carbothermal reduction which has (1) improved conversion rates of forming silicon carbide from carbon and silica sources, and (2) reduced operating costs due to use of less materials and smaller reactors required for the same product yields as the process of aforementioned PCT Patent Application No. PCT/US90/00276.
It is also an object of this invention to provide a process for making sinterable, high quality beta silicon carbide powder of uniform submicron size.